1. Field of the Invention
This invention relates to therapeutic agents, radiotherapeutic agents, radiodiagnostic agents, and non-radioactive diagnostic agents, and methods for producing such diagnostic and therapeutic agents. The invention also relates to cyclic peptides which specifically bind to somatostatin receptors expressed at the surface of mammalian cells, particularly neoplastic or metastatic mammalian cells. The invention in one aspect relates to scintigraphic imaging agents for imaging sites in a mammalian body. In this aspect, the imaging agents comprise a specific-binding peptide that specifically binds to somatostatin receptor-expressing cells in vivo, labeled with technetium-99m (Tc-99m) via a radiolabel-binding moiety which forms a complex with Tc-99m. In another aspect, the invention provides radioiodinated imaging agents. The invention also provides therapeutic agents, including radioiodinated agents, radioactive metal-reagent complexes and nonradioactive metal-reagent complexes, all of which have therapeutic utility. The invention provides reagents for preparing each of the diagnostic and therapeutic embodiments of the diagnostic and therapeutic agents of the invention, the radiolabeled embodiments and non-radioactive metal complexes thereof, methods for labeling said reagents and kits comprising non-radioactive embodiments of the reagents of the invention and other components for the convenient preparation of the radiolabeled diagnostic and therapeutic agents of the invention.
2. Description of the Prior Art
Somatostatin is a tetradecapeptide that is endogenously produced by the hypothalamus and pancreas in humans and other mammals. The peptide has the formula:
Formula I ##STR1## (Single letter abbreviations for amino acids can be found in G. Zubay, Biochemistry (2d ed.), 1988, (MacMillan Publishing: New York), p.33). This peptide exerts a wide variety of biological effects in vivo. It is known to act physiologically on the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract.
Somatostatin inhibits the release of insulin and glucagon from the pancreas, inhibits growth hormone release from the hypothalamus, and reduces gastric secretions. Thus, somatostatin has clinical and therapeutic applications for the alleviation of a number of ailments and diseases, both in humans and other animals. Native somatostatin is of limited utility, however, due to its short half-life in vivo, where it is rapidly degraded by peptidases. For this reason, somatostatin analogues having improved in vivo stability have been developed in the prior art.
Freidinger, U.S. Pat. No. 4,235,886 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy and Murphy, U.S. Pat. No. 4,485,101 disclose synthetic dodecapeptide somatostatin analogues.
Freidinger, U.S. Pat. No. 4,611,054 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Nutt, U.S. Pat. No. 4,612,366 disclose cyclic hexapeptide somatostatin analogues useful in the treatment of a number of diseases in humans.
Coy et al., U.S. Pat. No. 4,853,371 disclose synthetic octapeptide somatostatin analogues.
Coy and Murphy, U.S. Pat. No. 4,871,717 disclose synthetic heptapeptide somatostatin analogues.
Coy et al., U.S. Pat. No. 4,904,642 disclose synthetic octapeptide somatostatin analogues.
Taylor et al., U.S. Pat. No. 5,073,541 disclose a method of treating small cell lung cancer.
Brady, European Pat. Application No. 83111747.8 discloses dicyclic hexapeptide somatostatin analogues useful in the treatment of a number of human diseases.
Bauer et al., European Patent Application No. 85810617.2 disclose somatostatin derivatives useful in the treatment of a number of human diseases.
Eck and Moreau, European Patent Application No. 90302760.5 disclose therapeutic octapeptide somatostatin analogues.
Coy and Murphy, International Patent Application Serial No. PCT/US90/07074 disclose somatostatin analogues for therapeutic uses.
Schally et al., European Patent Application Serial No. EPA 911048445.2 disclose cyclic peptides for therapeutic use.
Bodgen and Moreau, International Patent Application Serial No. PCT/US92/01027 disclose compositions and methods for treating proliferative skin disease.
Somatostatin exerts effects by binding to specific receptors expressed at the cell surface of cells comprising the central nervous system, the hypothalamus, the pancreas, and the gastrointestinal tract. These high-affinity somatostatin binding sites have been found to be abundantly expressed at the cell surface of most endocrine-active tumors arising from these tissues.
It is frequently clinically advantageous for a physician to be able to localize the site of pathological conditions in a patient using non-invasive means. Such pathological conditions include diseases of the lungs, heart, liver, kidneys, bones and brain, as well as cancer, thrombosis, pulmonary embolism, infection, inflammation and atherosclerosis.
In the field of nuclear medicine, certain pathological conditions are localized, or their extent is assessed, by detecting the distribution of small quantities of internally-administered radioactively labeled tracer compounds (called radiotracers or radiopharmaceuticals). Methods for detecting these radiopharmaceuticals are known generally as imaging or radioimaging methods.
In radioimaging, the radiolabel is a gamma-radiation emitting radionuclide and the radiotracer is located using a gamma-radiation detecting camera (this process is often referred to as gamma scintigraphy). The imaged site is detectable because the radiotracer is chosen either to localize at a pathological site (termed positive contrast) or, alternatively, the radiotracer is chosen specifically not to localize at such pathological sites (termed negative contrast). In many situations it is a particular advantage to use a radiolabeled specific binding compound as a radiopharmaceutical which localizes specifically to the pathological site in vivo.
For example, expression of high-affinity binding sites for somatostatin is a marker for certain tumor cells, and specific binding with somatostatin can be exploited to locate and identify such tumor cells in vivo.
Methods for radiolabeling somatostatin analogues that have been modified so as to contain a tyrosine amino acid (Tyr or Y) are known in the prior art.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.123 I.
Bakker et al., 1990, J. Nucl. Med. 31: 1501-1509 describe radioactive iodination of a somatostatin analog and its usefulness in detecting tumors in vivo.
Bakker et al., 1991, J. Nucl. Med. 32: 1184-1189 teach the usefulness of radiolabeled somatostatin for radioimaging in vivo.
Bomanji et al., 1992, J. Nucl. Med. 33: 1121-1124 describe the use of iodinated (Tyr-3) octreotide for imaging metastatic carcinoid tumors.
Alternatively, methods for radiolabeling somatostatin by covalently modifying the peptide to contain a radionuclide-chelating group have been disclosed in the prior art.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.111 In via a chelating group bound to the amino-terminus.
Albert et al., International Patent Application No. WO 91/01144 disclose radioimaging using radiolabeled peptides related to growth factors, hormones, interferons and cytokines and comprised of a specific recognition peptide covalently linked to a radionuclide chelating group.
Albert et al., European Patent Application No. 92810381.1 disclose somatostatin peptides having amino-terminally linked chelators.
Faglia et al., 1991, J. Clin. Endocrinol. Metab. 73: 850-856 describe the detection of somatostatin receptors in patients.
Kwekkeboom et al., 1991, J. Nucl. Med. 32: 981 Abstract #305 relates to radiolabeling somatostatin analogues with .sup.111 In.
Albert et al., 1991, Abstract LM10, 12th American Peptide Symposium: 1991 describe uses for .sup.111 In-labeled diethylene-triaminopentaacetic acid-derivatized somatostatin analogues.
Krenning et al., 1992, J. Nucl. Med. 33: 652-658 describe clinical scintigraphy using .sup.111 In)(DTPA)octreotide.
A variety of radionuclides are known to be useful for radioimaging, including .sup.67 Ga, .sup.99m Tc (Tc-99m), .sup.111 In, .sup.123 I, .sup.125 I, .sup.169 Yb or .sup.186 Re. A number of factors must be considered for optimal radioimaging in humans. To maximize the efficiency of detection, a radionuclide that emits gamma energy in the 100 to 200 keV range is preferred. To minimize the absorbed radiation dose to the patient, the physical half-life of the radionuclide should be as short as the imaging procedure will allow. To allow for examinations to be performed on any day and at any time of the day, it is advantageous to have a source of the radionuclide always available at the clinical site. Tc-99m is a preferred radionuclide because it emits gamma radiation at 140 keV, it has a physical half-life of 6 hours, and it is readily available on-site using a molybdenum-99/technetium-99m generator. Other radionuclides used in the prior art are less advantageous than Tc-99m. This can be because the physical half-life of such radionuclides are longer, resulting in a greater amount of absorbed radiation dose to the patient (e.g., indium-111). Also, many disadvantageous radionuclides cannot be produced using an on-site generator.
Tc-99m is a transition metal that is advantageously chelated by a metal complexing moiety. Radiolabel complexing moieties capable of binding Tc-99m can be covalently linked to various specific binding compounds to provide a means for radiolabeling such specific binding compounds. This is because the most commonly available chemical species of Tc-99m, pertechnetate (TcO.sub.4.sup.-), cannot bind directly to most specific binding compounds strongly enough to be useful as a radiopharmaceutical. Complexing of Tc-99m with such radiolabel complexing moieties typically entails chemical reduction of the pertechnetate using a reducing agent such as stannous chloride.
The use of chelating agents for complexing Tc-99m is known in the prior art.
Byrne et al., U.S. Pat. No. 4,434,151 describe homocysteine containing chelating agents for Tc-99m.
Fritzberg, U.S. Pat. No. 4,444,690 describes a series of technetium-chelating agents based on 2,3-bis(mercaptoacetamido) propanoate.
Byrne et al., U.S. Pat. No. 4,571,430 describe homocysteine containing chelating agents for Tc-99m.
Byrne et al., U.S. Pat. No. 4,575,556 describe homocysteine containing chelating agents for Tc-99m.
Nosco et al., U.S. Pat. No. 4,925,650 describe Tc-99m chelating complexes.
Kondo et al., European Patent Application, Publication No. 483704 A1 disclose a process for preparing a Tc-99m complex with a mercapto-Gly-Gly-Gly moiety.
European Patent Application No. 84109831.2 describes bisamido, bisthiol Tc-99m ligands and salts thereof as renal function monitoring agents.
Davison et al., 1981, Inorg. Chem. 20: 1629-1632 disclose oxotechnetium chelate complexes.
Fritzberg et al., 1982, J. Nucl. Med. 23: 592-598 disclose a Tc-99m chelating agent based on N,N'-bis(mercaptoacetyl)-2,3-diaminopropanoate.
Byrne et al., 1983, J. Nucl. Med. 24: P126 describe homocysteine containing chelating agents for Tc-99m.
Bryson et al., 1988, Inorg. Chem. 27: 2154-2161 describe neutral complexes of technetium-99 which are unstable to excess ligand.
Misra et al., 1989, Tet. Lett. 30: 1885-1888 describe bisamine bisthiol compounds for radiolabeling purposes.
The use of chelating agents for radiolabeling specific-binding compounds is known in the art.
Gansow et al., U.S. Pat. No. 4,472,509 teach methods of manufacturing and purifying Tc-99m chelate-conjugated monoclonal antibodies.
Stavrianopoulos, U.S. Pat. No. 4,943,523 teach detectable molecules comprising metal chelating moieties.
Fritzberg et al., European Patent Application No. 86100360.6 describe dithiol, diamino, or diamidocarboxylic acid or amine complexes useful for making technetium-labeled imaging agents.
Albert et al., UK Patent Application 8927255.3 disclose radioimaging using somatostatin derivatives such as octreotide labeled with .sup.111 In via a chelating group bound to the amino-terminus.
Albert et al., International Patent Application, Publication No. WO 91/01144 disclose radioimaging using radiolabeled peptides related to growth factors, hormones, interferons and cytokines and comprised of a specific recognition peptide covalently linked to a radionuclide chelating group.
Fischman et al., International Patent Application, Publication No. WO93/13317 disclose chemotactic peptides attached to chelating moieties.
Kwekkeboom et al., 1991, J. Nucl. Med. 32: 981 Abstract #305 relates to radiolabeling somatostatin analogues with .sup.111 In.
Albert et al., 1991, Abstract LM10, 12th American Peptide Symposium: 1991 describe uses for .sup.111 In-labeled diethylene-triaminopentaacetic acid-derivatized somatostatin analogues.
Cox et al., 1991, Abstract, 7th International Symposium on Radiopharmacology, p. 16, disclose the use of, Tc-99m-, .sup.131 I- and .sup.111 In-labeled somatostatin analogues in radiolocalization of endocrine tumors in vivo by scintigraphy.
Methods for labeling certain specific-binding compounds with Tc-99m are known in the prior art.
Hnatowich, U.S. Pat. No. 4,668,503 describe Tc-99m protein radiolabeling.
Tolman, U.S. Pat. No. 4,732,684 describe conjugation of targeting molecules and fragments of metallothionein.
Nicolotti et al., U.S. Pat. No. 4,861,869 describe bifunctional coupling agents useful in forming conjugates with biological molecules such as antibodies.
Fritzberg et al., U.S. Pat. No. 4,965,392 describe various S-protected mercaptoacetylglycylglycine-based chelators for labeling proteins.
Schochat et al., U.S. Pat. No. 5,061,641 disclose direct radiolabeling of proteins comprised of at least one "pendent" sulfhydryl group.
Fritzberg et al., U.S. Pat. No. 5,091,514 describe various S-protected mercaptoacetylglycylglycine-based chelators for labeling proteins.
Gustavson et al., U.S. Pat. No. 5,112,953 disclose Tc-99m chelating agents for radiolabeling proteins.
Kasina et al., U.S. Pat. No. 5,175,257 describe various combinations of targeting molecules and Tc-99m chelating groups.
Dean et al., U.S. Pat. No. 5,180,816 disclose methods for radiolabeling a protein with Tc-99m via a bifunctional chelating agent.
Sundrehagen, International Patent Application, Publication No. WO85/03231 disclose Tc-99m labeling of proteins.
Reno and Bottino, European Patent Application 87300426.1 disclose radiolabeling antibodies with Tc-99m.
Bremer et al., European Patent Application No. 87118142.6 disclose Tc-99m radiolabeling of antibody molecules.
Pak et al., International Patent Application, Publication No. WO 88/07382 disclose a method for labeling antibodies with Tc-99m.
Goedemans et al., International Patent Application, Publication No. WO 89/07456 describe radiolabeling proteins using cyclic thiol compounds, particularly 2-iminothiolane and derivatives.
Dean et al., International Patent Application, Publication No. WO89/12625 teach bifunctional coupling agents for Tc-99m labeling of proteins.
Schoemaker et al., International Patent Application, Publication No. WO90/06323 disclose chimeric proteins comprising a metal-binding region.
Thornback et al., EPC Application No. 90402206.8 describe preparation and use of radiolabeled proteins or peptides using thiol-containing compounds, particularly 2-iminothiolane.
Gustavson et al., International Patent Application, Publication No. WO91/09876 disclose Tc-99m chelating agents for radiolabeling proteins.
Rhodes, 1974, Sem. Nucl. Med. 4: 281-293 teach the labeling of human serum albumin with technetium-99m.
Khaw et al., 1982, J. Nucl. Med. 23: 1011-1019 disclose methods for labeling biologically active macromolecules with Tc-99m.
Schwartz et al., 1991, Bioconjugate Chem. 2: 333 describe a method for labeling proteins with Tc-99m using a hydrazinonicotinamide group.
Attempts at radiolabeling peptides have been reported in the prior art.
Ege et al., U.S. Pat. No. 4,832,940 teach radiolabeled peptides for imaging localized T-lymphocytes.
Morgan et al., U.S. Pat. No. 4,986,979 disclose methods for imaging sites of inflammation.
Flanagan et al., U.S. Pat. No. 5,248,764 describe conjugates between a radiolabel chelating moiety and atrial natiuretic factor-derived peptides.
Ranby et al., 1988, PCT/US88/02276 disclose a method for detecting fibrin deposits in an animal comprising covalently binding a radiolabeled compound to fibrin.
Lees et al., 1989, PCT/US89/01854 teach radiolabeled peptides for arterial imaging.
Morgan et al., International Patent Application, Publication No. WO90/10463 disclose methods for imaging sites of inflammation.
Flanagan et al., European Patent Application No. 90306428.5 disclose Tc-99m labeling of synthetic peptide fragments via a set of organic chelating molecules.
Stuttle, PCT Application, Publication No. WO 90/15818 describes Tc-99m labeling of RGD-containing oligopeptides.
Rodwell et al., 1991, PCT/US91/03116 disclose conjugates of "molecular recognition units" with "effector domains".
Cox, International Patent Application No. PCT/US92/04559 discloses radiolabeled somatostatin derivatives containing two cysteine residues.
Rhodes et al., International Patent Application, Publication No. WO93/12819 teach peptides comprising metal ion-binding domains.
Lyle et al, International Patent Application, Publication No. WO93/15770 disclose Tc-99m chelators and peptides labeled with Tc-99m.
Coughlin et al, International Patent Application, Publication No. WO93/21151 disclose bifunctional chelating agents comprising thiourea groups for radiolabeling targeting molecules.
Knight et al., 1990, 37th Annual Meeting of the Society of Nuclear Medicine, Abstract #209, claim thrombus imaging using Tc-99m labeled peptides.
Babich et al., 1993, J. Nucl. Med. 34: 1964-1974 describe Tc-99m labeled peptides comprising hydrazinonicotinamide derivatives.
Methods for directly labeling somatostatin, derivatives of somatostatin, analogues of somatostatin or peptides that bind to the somatostatin receptor and contain at least 2 cysteine residues that form a disulfide or wherein the disulfide is reduced to the sulfhydryl form, are disclosed in co-owned U.S. Pat. No. 5,225,180, issued Jul. 6, 1993 which is hereby incorporated by reference in its entirety.
The use of chelating agents for radiolabeling peptides, and methods for labeling peptides with Tc-99m are known in the prior art and are disclosed in co-pending U.S. patent applications Ser. Nos. 07/653,012, now abandoned, which issued as U.S. Pat. No. 5,811,394; 07/807,062, now U.S. Pat. No. 5,443,815; 07/871,282; 07/893,981, now U.S. Pat. No. 5,508,020; 07/955,466, now abandoned; 08/092,355; and 08/095,760, now U.S. Pat. No. 5,620,675.
There remains a need for synthetic (to make routine manufacture practicable and to ease regulatory acceptance) somatostatin analogues having increased in vivo stability, to be used therapeutically, as scintigraphic agents when radiolabeled with Tc-99m or other detectable radioisotopes for use in imaging tumors in vivo, and as radiotherapeutic agents when radiolabeled with a cytotoxic radioisotope such as rhenium-188. Small synthetic somatostatin analogues are provided by this invention that specifically fulfill this need.